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Electrical and Optical Properties of Titanium‐Doped Lithium Fluoride Crystals
Author(s) -
Jain S. C.,
Sootha G. D.
Publication year - 1967
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19670220223
Subject(s) - vacancy defect , titanium , materials science , lithium fluoride , analytical chemistry (journal) , doping , absorption (acoustics) , electrical resistivity and conductivity , band gap , activation energy , absorption band , lithium (medication) , crystallography , inorganic chemistry , chemistry , optics , metallurgy , optoelectronics , physics , composite material , medicine , quantum mechanics , endocrinology , chromatography
Measurements are made of the electrical conductivity and optical absorption of LiF crystals doped with Ti. The plot of log (σ T ) as a function of 1/ T shows the usual intrinsic and extrinsic regions. In the extrinsic region, the behaviour of titanium is found to be similar to that of magnesium but different from that of manganese. The results indicate that most of the titanium is present in a highly aggregated form. However, a small fraction of the titanium is atomically dispersed in the form of doubly positively charged centres, either as Ti 2+ or as stable pairs of Ti 3+ and a cation vacancy. The values of the energies derived from the conductivity plot are W = 2.74 eV for the energy of formation of a separated pair of vacancies, E = 0.70 eV for the activation energy for the migration of a cation vacancy, and W a = 0.48 eV for the energy of association of a cation vacancy with a titanium centre. Unirradiated LiF:Ti crystals show an optical absorption band, designated as the E‐band, at 207 nm with a half‐width of 0.72 eV. On X‐irradiation, this band decreases, and the F‐band and two new bands are observed. The new bands are designated as the H‐ and G‐bands. The H‐band occurs at 240 nm with a half‐width of 0.20 eV and the G‐band at 270 nm with a half‐width of 0.25 eV. The rate of growth of the F‐band on X‐irradiation is enhanced considerably by titanium impurity. Possible models of the E‐, G‐ and H‐centres are discussed and approximate values of the appropriate oscillator strengths are: f F = 0.32, f E = 0.23, and f G = 0.07. Attempts to distinguish between Ti 2+ , and Ti 3+ plus a cation vacancy, by ESR absorption measurements are not successful because the titanium in highly aggregated form gives a very strong, complicated, and temperature independent background to the ESR absorption. Experiments are suggested which would distinguish between the two possible models of the titanium centres.